Scroll type machines are becoming more and more popular for use as compressors in both refrigeration as well as air conditioning applications due primarily to their capability for extremely efficient operation. Generally, these machines incorporate a pair of intermeshed spiral wraps, one of which is caused to orbit relative to the other so as to define one or more moving chambers which progressively decrease in size as they travel from an outer suction port toward a center discharge port. An electric motor is provided which operates to drive the orbiting scroll member via a suitable drive shaft affixed to the motor rotor. In a hermetic compressor, the bottom of the hermetic shell normally contains an oil sump for lubricating and cooling purposes.
In order to expand the use of scroll type machines and to increase the efficiency of these machines, capacity modulation systems have been developed to vary the capacity of these machines. A wide variety of systems have been developed in order to accomplish capacity modulation most of which delay the initial sealing point of the moving fluid pockets defined by the scroll members. In one form, such systems commonly employ a pair of vent passages communicating between suction pressure and the outermost pair of moving fluid pockets. Typically these passages open into the moving fluid pockets at a position normally within 360.degree. of the sealing point of the outer ends of the wraps. Some systems employ a separate valve member for each such vent passage. These valves are intended to be operated simultaneously so as to ensure a pressure balance between the two fluid pockets. Other systems employ additional passages to place the two vent passages in fluid communication thereby enabling use of a single valve to control capacity modulation.
More recently a capacity modulation system for scroll compressors of the delayed suction type has been developed in which a valving ring is movably supported on the non-orbiting scroll member. An actuating piston is provided which operates to rotate the valving ring relative to the non-orbiting scroll member to thereby selectively open and close one or more vent passages which communicate with selective ones of the moving fluid pockets to thereby vent the pockets to suction. A scroll-type compressor incorporating this type of capacity modulation system is disclosed in U.S. Pat. No. 5,678,985 the disclosure of which is hereby incorporated by reference. In this capacity modulation system, the actuating piston is operated by fluid pressure controlled by a solenoid valve.
This capacity modulation system utilizes a pair of axially extending passages in the non-orbiting scroll that place a pair of the moving pockets in fluid communication with the suction pressure zone of the compressor in order to delay the sealing of the moving pockets and thus reduce the capacity of the scroll machine. The delay in the sealing for the pockets reduces the capacity of the scroll machine and therefore reduces the fluid pressure within the pockets when compared with the pressure within the fluid pockets when the compressor is operating in the full load mode. In a scroll compressor which utilizes compressed fluid from the moving pockets to bias the two scroll members together, the reduced pressure within the pockets reduces the fluid pressure biasing the scroll members together which then potentially creates the problem of the scroll members unloading.
In compressors which utilize a floating seal which is biased to close a leakage path between discharge and suction, a similar problem could be created. A lower fluid pressure lowers the biasing load for the seal which potentially creates the problem of the seal falling to open the leakage path between discharge and suction thus unloading the compressor.
In order to prevent unloading of the scroll compressor when the capacity modulation system is actuated, the bleed hole which supplies the biasing fluid for the biasing chamber needs to be moved closer to the discharge port of the compressor. This movement of the bleed hole closer to the discharge port will increase the biasing fluid pressure in both the modulation mode as well as in the full capacity mode. While moving the bleed hole closer to discharge may help resolve the problems associated with compressor unloading during modulated operation, the increase biasing pressurized fluid during full load operation can create other problems with the operation of the compressor. These problems include but are not limited to an increase in the pressure pulsation in the intermediate chamber and an increase in the compression power required.
The present invention provides the art with a bleed hole which allows a relatively large flow of pressurized fluid from the fluid pockets to the intermediate chamber while limiting the flow of pressurized fluid from the intermediate chamber back to the fluid pockets. In one embodiment, this bleed hole is used in conjunction with a capacity modulation system which then allows for the normal placement for the bleed hole. In another embodiment of the present invention, this bleed hole is used in a non-modulated compressor in order to decrease the pressure pulsation in the intermediate chamber.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.